Self-holding type solenoid valves

Abstract: A self-holding type solenoid valve has an exciting coil 13 and an exciting circuit 3 that switches the direction of flow of exciting current passing through the coil. When a positive exciting current flows through the coil 13, a movable iron core 18 is attracted to a stationary iron core 15 and held in the attracted position by a self-contained permanent magnet 14. When a reversed current flows through the coil 13, a return spring 19 releases the movable iron core 18 away from the stationary iron core 15.

Description: This invention relates to a self-holding type solenoid valve which maintain its operating condition by means of a permanent magnet. One example of such a self-holding type solenoid valve employing a permanent magnet is disclosed in Japanese Provisional Patent Publication JP-A-63297883, which forms a basis for the preamble of claim 1. This self-holding type solenoid valve comprises a main valve segment including a valve member that switches the direction of flow of fluid between multiple ports and a solenoid segment that actuates the valve member. The solenoid segment comprises a bobbin surrounded by two coils of wire, a magnetic frame and a magnetic plate surrounding the bobbin, a stationary iron core and a self-holding permanent magnet fitted to the centre hole in the bobbin, and a movable iron core slidably fitted in the same centre hole in the bobbin. When one of the two coils of wire is energized, the movable iron core is attracted to the stationary iron core, whereupon the valve member moves to switch the flow of liquid between the ports and the self-contained permanent magnet holds the movable iron core in the attracted position. When the other coil is energised, the movable iron core is released from the stationary iron core and the valve member returns to its original position. The conventional self-holding type solenoid valve just described requires two coils of wire, one attracting the movable iron core to the stationery iron core and the other releasing the movable iron core from the attracted position in which it is held by means of the self-contained permanent magnet. Because two coils occupy a large space, the solenoid segment and the solenoid valve become larger than is desired. EP-A-219572 shows an electrically operated vacuum valve with a single coil. An actuating member is attracted to a permanent magnet when the coil is energised in one direction and then held by the permanent magnet and is released and moves away from the permanent magnet when the coil is energised in the reverse direction. A primary object of this invention is to provide a small and simple self-holding type solenoid valve that provides a function to attract a movable iron core to a stationery iron core and a function to release the movable iron core from the attracted position with only one coil. According to the invention there is provided a self-holding type solenoid valve comprising a main valve segment having multiple ports and a valve member to switch the communication therebetween, a solenoid segment comprising a coil wound around a bobbin, a stationary iron core and a permanent magnet fastened in a centre hole in the bobbin, a moveable iron core for actuating the valve member and inserted in the centre hole in such a manner as to be slidable toward and away from the stationery iron core, and a return spring urging the movable iron core away from the stationary iron core, the movable iron core being attracted to the stationary iron core when a forward energising current flows through the coil, and being held thereagainst by the permanent magnet, characterised by: an energising circuit for supplying an energising current in the forward or reverse direction of flow through the coil, the movable iron core being released away from the stationary iron core when a reversed energizing current flows through the coil, a step on the stationary iron core engaging with a step in the centre hole in the bobbin, the permanent magnet being mounted at the back of the stationary iron core, and the stationary iron core and permanent magnet being fastened in the centre hole by means of a set nut of ferromagnetic material that presses the permanent magnet against the stationary iron core, the set nut being screwed into a magnet frame surrounding the bobbin and forming a part of a magnetic path. According to one preferred embodiment a screw is driven into the seat nut to fasten a plate to the outside of the solenoid. The plate thus fastened forms a case that contains a printed circuit board carrying the energising circuit. When the energising circuit passes the energising current in the forward direction, a resultant force comprising the magnetic forces generated by the coil and the permanent magnet attracts the movable iron core to the stationary iron core, whereupon the valve segment moves to switch the direction of flow of fluid between the multiple ports. Even if the exciting current is subsequently cut off, the self-contained permanent magnet keeps the movable iron core in the attracted position and the valve segment in the switched position. When the direction of the energising current is reversed, the magnetic forces generated by the coil and the permanent magnet offset each other, thereby decreasing the attraction force between the movable and stationary iron cores, whereupon the force exerted by the return spring releases the movable iron core away from the stationary iron core. Then, the valve member also moves to switch the direction of flow of fluid. Thus, the self-holding type solenoid valve of this invention with only one coil achieves the attraction of the movable iron core to the stationary iron core and the release of the former away from the latter by switching the direction of the energising current passed therebetween. This feature permits designing small and simple self-holding type solenoid valves. The valve can also be of high magnetic efficiency and fast response. The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a vertical from view of a self-holding type solenoid valve according to this invention; Fig. 2 is a diagram showing an energising circuit used with the valve according to this invention; and Fig. 3 is a diagram showing another energising circuit. Fig. 1 shows a self-holding type solenoid valve according to this invention comprising a main valve segment 1 having a valve member 7 that switches the direction of flow of compressed air, a solenoid segment 2 that actuates the valve member 7, and an exciting circuit 3 that controls the exciting current supplied to the solenoid segment 2. The main valve segment 1 comprises a valve body 4 that has an inlet port P, an outlet port A and a discharge port R through which the compressed air flows. An inlet valve seat 5 between the outlet port A and the inlet port P and a discharge valve seat 6 between the outlet port A and the discharge port R are located opposite each other. The valve member 7 is disposed between the two valve seats 5 and 6 and is urged toward the discharge valve seat 6 by a valve spring 8 interposed between the valve member 7 and the valve body 4. The face of the valve member 7 on the side of the discharge valve seat 6 is in contact with the tip of a movable iron core 18 projecting from the solenoid segment 2. The solenoid segment 2 comprises a magnetic frame 10 and a magnetic plate 11 that, in combination, form a magnetic path, a bobbin 12 contained within the magnetic frame 10 and plate 11, a coil of wire 13 wound around the bobbin 12, and a self-holding permanent magnet 14 and a stationary iron core 15 that are fastened in a center hole 12a in the bobbin 12. The permanent magnet 14 and stationary iron core 15 are fastened in the centre hole 12a by engaging a step 15a on the stationary iron core 15 with a step 12b in the centre hole 12a, with the permanent magnet 14 placed behind the stationary iron core 15 pressed against the stationary iron core 15 by means of a set nut 16 of ferromagnetic material screwed into the magnetic frame 10. This fastening method permits the stationary iron core 15 to be always fastened in a fixed position even when the permanent magnet 14 is not made exactly to the design size specification, thus keeping the stroke of the movable iron core 18 within the preset range. It also ensures that the stationary iron core 15 and the permanent magnet 14 are always kept in close contact with each other, thereby decreasing the flux leakage. The set nut 16 that is made of ferromagnetic material and forms a part of the magnetic path increases the magnetic efficiency of the permanent magnet 14. The movable iron core 18 is inserted in the centre hole 12a in the bobbin 12 in such a manner as to come in and out of contact with the stationary iron core 15. A return spring 19 placed between the movable iron core 18 and the magnetic plate 11 urges the movable iron core 18 away from the stationary iron core 15. The tip of the movable iron core 18 passes through the discharge valve seat 6 and comes in contact with the valve member 7, thus pressing the valve member 7 against the inlet valve seat 5 when the coil is not energised. A moulding 20 of electrically insulating resin covers the outside of the magnetic frame 10. A fitting bolt 22 screwed through the set nut 16 fastens a plate 23 to the outside of the moulding 20. A case 24 attached to one side of the plate 23 contains a printed circuited board 26 carrying electric and electronic components 25. Electricity is supplied from a socket 28 to three power-supply terminals 27 (only one of them is shown) that are electrically connected to a printed circuit on the printed circuit board 26. Fig. 2 shows an example of the energising circuit 3 for energising the coil 13. The energising circuit 3 is formed on the surface of the printed circuit board 26 and has a setting terminal 27A, a resetting terminal 27B and a common terminal 27C. When a switch SW is actuated to connect the common terminal 27C to the setting terminal 27A, base current flows through a resistor R 1 to a transistor T 1 , whereupon the emitter and collector of the transistor T 1 are electrically connected to pass current from C 1 to C 2 of the coil 13 and C 1 and C 2 of the coil 13 are defined as a south and a north pole. When the polarity of the permanent magnet 14 is made equal to that of the coil 13, therefore, the attraction forces of the coil 13 and permanent magnet 14 are combined into a strong composite force that attracts the movable iron core 18 to the stationary iron core 15. At the same time, the valve member 7 urged by the valve spring 8 opens the inlet valve seat 5 and closes the discharge valve seat 6. Once the movable iron core 18 has been attracted to the stationary iron core 15, the attraction force of the permanent magnet 14 keeps the movable iron core 18 in the attracted position and the valve member 7 in the actuated position described before, thereby allowing the fluid to flow in the same direction, even if the current supply from the energising circuit 3 is cut off. When the switch SW connects the common terminal 27C to the resetting terminal 27B, base current flows through a resistor R 2 to a transistor T 2 , thereby electrically connecting the emitter and collector of the transistor T 2 , passing current from C 2 to C 1 of the coil 13, and thus reversing the polarity thereof. As a consequence, the attraction forces of the permanent magnet 14 and coil 13 repel and offset each other. Then, the force with which the movable iron core 18 is attracted to the stationary iron core 15 becomes smaller than the urging force the return spring 19. Therefore, the movable iron core 18 is released from the attracted position and urged back to the illustrated position by the return spring 19. Pushed by the movable iron core 18, the valve member 7 returns to the illustrated position, thereby opening the discharge valve seat 6 and closing the inlet valve seat 5. As described above, the self-holding type solenoid valve having the permanent magnet 14 and the single coil 13 causes the movable iron core 18 to be attracted to the stationary iron core 15 and held in attracted position and released therefrom by switching the direction of flow of electric current passing through the coil 13. Fig. 3 shows another example of the energising circuit 3. This energising circuit 30 has a protective function that keeps diodes, transistors and other circuit components from burning out even when both terminals 27A and 27B are simultaneously connected to the common terminal 27C by some program error or other causes. When the switch SW in the circuit 30 connects the common terminal 27C to the setting terminal 27A, the transistor T 2 remains unexcited because the base of the transistor T 2 is grounded and the current I 6 passing through a resistor R 6 flows to the terminal 27A and not to the base of the transistor T 2 . On the other hand, the current I 8 passing through a resistor R 8 flows to the base of the transistor T 1 to excite the transistor T 1 as the setting terminal 27B is kept open. Therefore, the current from the terminal 27C flows through the transistor T 1 and the coil 13, from C 1 to C 2, and then to the terminal 27A. When the common terminal 27C is connected to the setting terminal 27B, the transistor T 1 becomes deexcited, while the current I 6 flowing through the resistor R 6 excites the transistor T 2 . Then, the current from the terminal 27C flows through the transistor T 2 and from C 2 to C 1 through the coil 13. Even when both terminals 27A and 27B are simultaneously connected to the common terminal 27C by some unexpected cause, the current I 6 flows to the terminal 27A while the current I 8 flows to the terminal 27B. Therefore, the base current does not flow to either of the transistors T 1 and T 2 which are thus kept unexcited. Consequently, the energising current does not flow through the coil 13, and the solenoid valve gives rise to no malfunction. Burning out of the transistors T 1 and T 2 , power supply unit and other apparatus can be prevented by making the resistance of the resistors R 6 and R 8 large enough while keeping bypass currents I 6 and I 8 at approximately 10 mA. When current is passed through the coil 13 in the self-holding type solenoid valve thus constructed, the stationary iron core 15 attracts the movable iron core 18. Then, the valve member 7 opens the inlet valve seat 5, while the magnetic force of the permanent magnet 14 keeps the movable iron core 18 in the attracted position. Therefore, the valve member 7 keeps open the inlet valve seat 5 even when the current supply to the coil 13 is cut off by program or by power failure or other accidents. Provision of the permanent magnet 14 in the centre hole 12a in the bobbin permits making the size of the solenoid segment 2 smaller than that on the conventional solenoid valves whose permanent magnet 14 is mounted outside on the outside of the magnetic frame 10. This design also decreases the leakage flux from the permanent magnet 14 and increases the attraction force by approximately 10 percent. Furthermore, the single coil 13 in the solenoid segment 2 serves the dual function of attracting the movable iron core 18 to the stationary iron core 15 and of releasing the movable iron core 18 away from the position in which it is kept by the force of the permanent magnet 14 by switching the direction of flow of electric current passing therethrough. Therefore, this dual-function single coil requires only half as much coiling space, as compared with the conventional two coils individually performing one of the two functions described above. This results in a smaller solenoid segment and a smaller self-holding type solenoid valve. If the single coil used is made as large as the combined two coils of a conventional bobbin, approximately twice as large an attraction force will be obtained.

Claims: A self-holding type solenoid valve comprising a main valve segment (1) having multiple ports (P, A, R) and a valve member (7) to switch the communication therebetween, a solenoid segment (2) comprising a coil (13) wound around a bobbin (12), a stationary iron core (15) and a permanent magnet (14) fastened in a centre hole (12a) in the bobbin (12), a moveable iron core (18) for actuating the valve member (7) and inserted in the centre hole (12a) in such a manner as to be slidable toward and away from the stationery iron core (15), and a return spring (19) urging the movable iron core (18) away from the stationary iron core (15), the movable iron core (18) being attracted to the stationary iron core (15) when a forward energising current flows through the coil, and being held thereagainst by the permanent magnet (14), characterised by: an energising circuit (3) for supplying an energising current in the forward or reverse direction of flow through the coil (13), the movable iron core (18) being released away from the stationary iron core (15) when a reversed energising current flows through the coil (13), a step (15a) on the stationary iron core (15) engaging with a step (12b) in the centre hole (12a) in the bobbin (12), the permanent magnet (14) being mounted at the back of the stationary iron core (15), and the stationary iron core (15) and permanent magnet (14) being fastened in the centre hole (12a) by means of a set nut (16) of ferromagnetic material that presses the permanent magnet (16) against the stationary iron core (15), the set nut (16) being screwed into a magnet frame (10) surrounding the bobbin (12) and forming a part of a magnetic path. A self-holding type solenoid valve as claimed in Claim 1 in which a bolt (22) screwed into the set nut (16) fastens a plate (23) to the outside of the solenoid segment (2) and a case (24) formed on the plate contains a printed circuit board (26) carrying the energising circuit (3).

Inventors: AZUMA SHINICHI, FUKANO YOSHIHIRO, NISHIBE ATSUSHI, AZUMA, SHINICHI, FUKANO, YOSHIHIRO, NISHIBE, ATSUSHI
Applicants: SMC CORP, SMC CORPORATION
Application year: 1994
Main classification: F16K31
IPC codes: F16K31, H01H47